1. Field of the Invention
This invention relates to an apparatus for photographing the endothelial layer of the cornea of a patient's eye by projecting illumination light onto the cornea.
2. Description of the Prior Art
Heretofore, there is known a contact type of apparatus for observing and photographing a corneal endothelium. In this type of apparatus, a liquid anesthetic is dropped into the eye before observing and photographing the endothelium therewith. The contact type of apparatus includes a cone lens which is in contact with the surface of the cornea. The apparatus, however, has drawbacks in that the cone lens injures the cornea because of contact of the lens with the corneal surface and much time is consumed for photography because of disinfection of the lens or the like. To remove those drawbacks, a non-contact type of apparatus has been developed in which a slit lamp is provided with an optical attachment for observing the endothelial layer.
The non-contact type of apparatus can generally determine its position relative to the eye in eye estimation. In the non-contact type of apparatus, illumination light emitted by a light source for observation is projected onto the cornea at an angle, reflected light from the cornea is guided to an eyepiece, and an operator observes the endothelial layer through the eyepiece and brings it into focus. A monitor screen can be also employed to take the focus.
By the way, the cornea itself is thin and its endothelium is composed of a single layer of thin flattened cells that lines the innermost portion of the cornea. Therefore, the endothelial layer must be highly magnified for observation. However, such a high magnification results in a big tremble of its image caused by involuntary movement of the eye (i.e., continuous slight motion of the eye when the eye is fixed). Therefore, the operator requires great skill to observe and photograph the corneal endothelial layer with the conventional non-contact type of apparatus. For example, the operator must act in a timely manner by pushing a photographing button as soon as the image is brought into focus. Further, since the non-contact type of apparatus is not predetermined to be precisely positioned relative to the eye, the operator must observe the dark field visible through the eyepiece until the image of the corneal endothelium appears or reflected light from the corneal surface is found out beside the image. This conventional apparatus largely depends on an operator's experience and strong intuitive judgement.
Further, since the alignment of the optical systems of the apparatus with the eye often requires much time, the patient is compelled for a long time to keep the eye open until photographing is completed, and hence undergoes much discomfort or pain.